No. Dimensional Slide "is used as part of a move action or withdraw action...". A 5' step is neither of these. Now, because of how Pathfinder has chosen to word stuff, it's a bit unclear if the referred to "move action" has to be literally moving, or any action that uses a "move action" such as drawing a weapon (with BAB 0 or when not doing it in conjunction with a "regular move"). While the terms are unfortunate, this particular power suffers less from this confusing terminology as it goes on to say "This counts as 5 feet of movement". So if a "move action" in this context is not the same as a "regular move", it at least must be one that also involves allowing you to move 5'.
That was sort of a derailment in that I essentially posed another question/problem in answering yours, so I'd like to reiterate the answer to your specific question here to make it clear: no, you cannot dimensional slide as a five-foot step.
